Is laughter contagious?

I love watching the funny videos on youtube and other places on the internet, and today I found a laughter chain being done by the folks at skype. If you go to the site, you can see the complete chain, and if you have a webcam, you can add yourself to the project. Within this chain is a man I’ve seen on youtube. His clip is titled Dad at the comedy barn.

There are a number of spin-offs from this clip, and this one is a girl laughing while watching him. I started to wonder how contagious laughter is, so I followed a long string of the spin-offs that left me breathless from laughter.

So my question is, what makes you laugh? Are you able to restrain your laughter when the person next to you is in hysterics? Please use this thread to share funny videos or jokes, etc. Let’s all have some giggles today.